It seems you did just fine. You gave a chance (and a second and third one) to a potential suitor, it didn't click, then you moved on. This is normal and it happens all the time. It is part of the process for choosing someone. You did not let go of a catch at all. You were lukewarm from the beginning and gave the guy plenty of opportunities to woo you. He didn't. I don't quite understand why you beat yourself over it. I don't even see a link with your recent breakup. What you just had was a normal, healthy dating experience. Well done for not going further!
You shouldn't go to dates wondering if he's the One (a concept I've never heard outside the US). If anything, if you want something serious, you should go to dates looking for reasons to dump them. When you find one that you just can't let go despite your best attempts, because you truly truly want more of him, that's when you have a catch. You'll be elated you found someone like that, believe me!
If you try to be attracted be attracted to every man who cleans up well and has a job, you'll catch the first guy out of the bus. Attraction and love are very special feelings and while, in the long run, we may choose to love someone, it has to be built on a basis of strong mutual attraction. Don't force it or you'll be unhappy and turn into a WAW in no time.
Again, for most people, your recent experience would be very banal. Don't let it get to you. Move on to the next prospect whenever you're ready.
By the way, responding to guys who email you is not as good as browsing for guys who interest you. You shouldn't just be reactive in this very, very important life decision. Raise the bar and go for it!
M39 D6 D3 (at S) S 2014-09 D 2016-09
"You can't start a fire sitting around, crying over a broken heart" - Bruce Springsteen.